Honestly I think you should scrap customs all together. When someone makes a custom card there's usually already a card that exists in the game which does the same thing or has close to the same purpose. Custom archetype support is almost pointless since usually that archetype will get some type of support down the line (whether it be direct or indirect). 

I can agree with the sentiment of givin undersupported archetypes more cards but usually they just get more cards anyways.

Also, in the show, only the super rich and powerful had access to custom decks that no one else had access to. Givin everybody that luxury kind of defeats the purpose behind custom cards. They're supposed to demonstrate ones wealth and influence and it makes thw heroes victory over them all the more satisfyin when they figure out how to beat their seemingly invincible unique cards.